This invention relates to a rolling element string in which multiple rolling elements such as balls or rollers are arranged in a line and held rollably and which is used fitted for example in an endless raceway of a linear guide device or a ball screw device for unlimited sliding, and particularly to a rolling element string which can be freely bent or twisted in use and a linear guide device and a rolling element screw device using this rolling element string.
Known linear guide devices for guiding a movable body such as a table along a fixed body such as a bed include those made up of a track rail having a ball rolling groove, a slider which moves along the track rail and has a loaded-rolling groove facing this ball rolling groove and has a no-load rollway through which balls are circulated from one end of the loaded-rolling groove to the other, and multiple balls which roll between the slider and the track rail while supporting a load and circulate around an endless raceway formed by the loaded-rolling groove and the no-load rollway of the slider.
In a linear guide device of the related art constructed in this way, because the endless raceway of the slider is filled by the balls, when the slider moves along the track rail, mutually adjacent balls collide with and rub against each other as they circulate around the endless raceway, and consequently there has been the problem that the balls wear quickly and the life of the device is short.
As a device which solves this problem, a linear guide device wherein a ball string made up of multiple balls held in a line is fitted in the kind of endless raceway described above has been proposed (Japanese Unexamined Patent Publication No. H. 5-52217). As shown in FIG. 13 and FIG. 14, this ball string 100 is made by interposing spacers 102 between mutually adjacent balls 101 and connecting the spacers 102 together with a pair of belt members 103 extending in the direction in which the balls are aligned, and is manufactured by injection molding of a flexible resin with the balls 101 disposed inside the mold as cores.
A ball string 100 of the related art constructed in this way is fitted in an endless raceway 105 of a slider 104 as shown in FIG. 15 and circulates around the inside of the endless raceway, and as it does so, because the spacers 102 are interposed between adjacent balls 101, the balls are prevented from rubbing and colliding with each other and wear of the balls 101 is minimized.
However, in this related art ball string 100, because each of the spacers 102 is supported by the two balls 101, 101 positioned on either side of it, when due to bending or twisting of the ball string 100 the angle of abutment of the spacers 102 with the balls 101 changes greatly, there is a possibility of the balls 101 dropping out from between the spacers 102.
Thus, although the related art ball string does perform the function of a retainer for preventing balls from making contact with each other, it does not fully perform the function of a so-called ball holder for preventing balls from dropping out, and for this reason, in related art linear guide devices in which this kind of ball string is fitted, to completely prevent incidents of balls dropping out when the slider is removed from the track rail, countermeasures such as separately fitting a ball holder have had to be employed.
In this connection, as a ball string having a strengthened ball-holding function, the present inventors have already proposed a new ball string 112 (FIG. 16 and FIG. 17) wherein four belt members 111 formed in the shape of bands extending in the direction of alignment of balls 110 are bound between each pair of adjacent balls and by this means the balls 110 are restrained from four directions and prevented from falling out (Japanese Patent Application No. H.8-245314).
However, with this new ball string 112, when it is bent, compressive forces act on the belt members 111 positioned on the inner side of the bend and tensile forces act on the belt members 111 positioned on the outer side of the bend and these belt members 111 obstruct the free bending of the ball string 112, and consequently there has been the new problem that the smooth circulation of the ball string 112 inside the endless raceway is hindered.
Also, because the faces of the balls are equally divided up by the four belt members 111, when these balls 110 roll along a ball rolling groove of a track rail and a loaded-rolling groove of a slider the belt members 111 are liable to interfere with the ball rolling groove and the loaded-rolling groove, and to avoid this interference it has been necessary to form escape grooves in the ball rolling groove and the loaded-rolling groove to receive the belt members 111. Consequently, in a linear guide device or the like using a ball string 112 of this kind, there has been the problem that it is necessary to especially form escape grooves for receiving the belt members 111 in the ball rolling groove of the track rail and the loaded-rolling groove of the slider and the manufacturing cost increases correspondingly.